The objective is to describe the mechanism of pinocytosis induction in the amoeba Chaos chaos. Pinocytosis inducers cause a structural change in the plasma membrane which can be either time dependent or stable. This change appears to be primarily a thickening of the intermediate electron transparent lamella. Physiological and electron- microscopical experiments will be performed to quantitatively relate the structural changes to the type and concentration of the cationic pinocytosis inducer. The data will be used to construct a model of the amoeba membrane. Additional experiments will be undertaken to define the linkage between the plasma membrane and the cytoplasm, for organized contraction of the latter forms the pinocytosis tunnels and invagination, from the plasma membrane.